A Single File System: “The Science of Simplicity”

WHAT IF ENDODONTICS WERE SIMPLE? WHAT IF ENDODONTICS WERE EASY?
Well, endodontics is not simple. In fact, the more we know about the novelty and curvatures of the root canal systems, the more that we are aware of nature’s anatomic complexities. Endodontics is not easy, but it may be becoming easier. First, there is a better understanding of how and why endodontic treatment protocols are increasing endodontic predictability through educational tools such as new research with micro computer tomography (CT). Then there is the microscope that brought endodontics out of the dark and allowed dentists to design proper access cavities and successfully find the canals that make up the root canal system. Then there are known fundamental mechanics for following canals to length. New cleaning solutions and 3-dimensional (3-D) techniques have been developed. Then there were rotary shaping and 3-D obturation methods. And now, there is a single endodontic mechanical shaping system called WaveOne (DENTSPLY Tulsa Dental Specialties and DENTSPLY Maillefer).

The purpose of this article is to investigate if a single file system makes scientific sense.

A SINGLE FILE CONCEPT
A single file system is certainly simple in concept versus multiple files and sounds like it could be easier, too. The first question you should ask, however, before you “test drive” this new system head to head with what you are using now, is whether or not this file is safe. The authors report on the safety of a single file system and then the reader’s job is to test and experience for yourself its efficacy, efficiency, and single file effectiveness versus your current endodontic system. At the end of the article, the authors will invite you to design a test for yourself, as we believe that the best education in the world is your own. Now for the science…

CONTEXT
So think about it…one file to do all shaping. Does this sound too good to be true? Most of us have experienced that when it sounds too good to be true, it usually is. As dentists, we are not so naïve as to think that one size fits all. After all, like anything else in nature, no 2 root canals systems are the same. However, this type of oversimplification is not the WaveOne technique, technology, or thinking. The idea is instead that dentists are capable of thinking and following directions. Masterful dentists further know how, when, and why to use which tool (instrument). WaveOne is no exception. WaveOne is not Dumbo’s magic feather, a shortcut, or a miracle. WaveOne is, however, a simplified and excellent way to shape canals safely and predictably allowing successful cleaning and obturation.

Here is what you need to know. First, read what has already been written about a single file endodontic shaping system.^1-10 Second, follow the directions for use. Third, get trained. The 8 clinicians who were asked to design and build a single file system learned from each other how and when to use it effectively. The group has been motivated to teach, write instructional and scientific articles, and lecture about the right time and place to consider a single file approach.⁶ With the single file system using the ProTaper F2 (DENTSPLY Tulsa Dental Specialties) in uneven reciprocation, clinicians were achieving success prior to a specifically engineered single file system.

In 2008, the team designed a dedicated file for the single file technique and has the trade name on WaveOne. Recently, Dr. Cliff Ruddle6 wrote about the history, rationale, design, advanced alloy, movement, and shaping technique of the WaveOne single file technique. It was Professor Pierre Machtou from Paris, France, along with one of his students, who began their journey of experimenting with the single file system using the ProTaper F2 in uneven reciprocation motions, and they reported great success with it.

A FIRST INQUIRY INTO THE SCIENCE OF SIMPLICITY
Mandibular first and second molars were chosen for the single file design testing because the 2 mesial root canals were often fairly similar in length, size, and curvature. It was the best tooth to compare results that were side by side. Root canal systems were observed to be equally complex after more than 200 micro CT scannings done at Nova Southeastern University, College of Dental Medicine by Drs. Carmen Bonilla and Sergio Kuttler (Figure 1). This complex configuration validated that a simple “drill” is insufficient to find, follow, and shape delicate labyrinths such as root canal systems. Drs. Bonilla and Kuttler’s research again dramatically revealed endodontic anatomy is different for every tooth.

The team’s research also documented that the foraminal constriction of most of the canals of mandibular first and second molars are a file size No. 15 (Figures 2 and 3). This would suggest a reciprocation file, the size No. 25 at the tip, would allow both cleaning and shaping at the physiologic constriction most of the time. The single file primary file was designed with this consistency in mind.

The WaveOne single file system actually consists of 3 files, and the clinician must choose which single file is most suitable for the canal he or she is treating. The sizes are primary, small, and large (Figure 4). Given the shape of primary (25/08), one question is: Is this sufficient space for effective irrigation to remove necrotic debris, detached collagen, biofilm, and smear layer? Radiographically, it has been documented that a size No. 30 gauge side-vented irrigation syringe fits freely at depths just short of the physiologic terminus, thus producing a sufficient and effective irrigation throughout the entire length of the root canal system (Figure 5). Moreover, with new technology such as the EndoActivator (DENTSPLY Tulsa Dental Specialties), and Q-mix (DENTSPLY Tulsa Dental Specialties) dentists can achieve excellent results (Figure 6).

Because the WaveOne file is used in a mechanical “balanced force” type movement, the torque strength should not be exceeded and therefore could increase safety over rotary file systems. Adding the M-Wire nickel-titanium (Ni-Ti) gives the file even greater flexibility and is more forgiving than standard Ni-Ti, which makes the primary, small, and large files safer. The WaveOne files also have built in modified guiding tips as well as cutting blades which makes a combination of efficiency and a good Glidepath (DENTSPLY Tulsa Dental Specialties) “following” capacity (Figures 7 and 8).

Figure 1. Micro computed tomography (CT) with complex anatomy.	Figure 2. Apical constrictions measurements. Coronal-apical 3-dimensional (3-D) reconstruction view of a mesiolingual canal.
Figure 3. Apical constrictions measurements. Coronal-apical 3-D reconstruction view of a mesiobuccal canal.	Figure 4. WaveOne (DENTSPLY Tulsa Dental Specialties and DENTSPLY Maillefer) file sizes.
Figure 5. Radiograph showing a No. 30 gauge side vented needle penetration to the apical constriction.	Figure 6. Scanning electron microscope (SEM) of apical dentin.
Figure 7. SEM of modified guiding tip of WaveOne.	Figure 8. SEM of cutting blades of WaveOne.

Sterility was and is paramount in bringing a single file system to the marketplace. All WaveOne packages are contained in easy to open sterile packaging (Figure 9).

An important question to ask when considering the WaveOne single file system is conservation of tooth structure during root canal shaping. Because of the progressive geometries of WaveOne, similar to the progressive geometries of ProTaper, this single file system compares favorably to constant taper file systems when considering conservation of tooth structure (Figures 10a to 10c).

Figure 9. WaveOne sterile packaging.	Figure 10a. Comparison chart of file dimension compared to a .04 constant taper size No. 40 showing that tooth structure is more removed with the constant taper.
Figure 10b. Comparison chart of file dimension compared to a .06 constant taper size No. 40 showing that tooth structure is more removed with the constant taper.	Figure 10c. Comparison chart of file dimension compared to a .08 constant taper size No. 25 showing that tooth structure is more removed with the constant taper.
Figure 11. Cross section at 3 mm from D0 of WaveOne.	Figure 12. Cross section at 11 mm from D0 of WaveOne.
Figure 13. Micro CT research showing the center ability of WaveOne; because of its unique design and movements, micro CT shows the coronal portion of canals (upper left rectangle), in red original canal and in green canals prepared with WaveOne primary file.	Figure 14. Micro CT research showing the center ability of WaveOne; because of its unique design and movements, micro CT shows the middle portion of canals (upper left rectangle), in red original canal and in green canals prepared with WaveOne primary file.
Figure 15. Micro CT research showing the center ability of WaveOne; because of its unique design and movements, micro CT shows the apical portion of canals (upper left rectangle), in red original canal and in green canals prepared with WaveOne primary file.	Figure 16. E3 Motor for WaveOne.

Figure 17. ProMark Motor for WaveOne.

In order to increase efficiency while maintaining safety, the WaveOne primary file is 2 files in one. The horizontal cross section from D0 to D8 is designed for “following” the Glidepath, while the section from D9 to D16 is designed for cutting the more restrictive coronal radicular dentin (Figures 11 and 12).

Another important question for the reader should be what is the accuracy of WaveOne to follow the Glidepath?^11-13 In other words, what is the ability of the file to remain centered and therefore reduce the likelihood of overcutting in areas of thin furcal dentin? Micro CT research¹⁴ (Figures 13 to 15) again produced favorable results. Because of the unique design and recioprocation movements using designated motors (Figures 16 and 17), the WaveOne file again performed positively by accurately measuring and comparing the original canal dimensions with the prepared canal dimensions.

CLOSING COMMENTS
A single file system appears to warrant its use and immediate consideration for the endodontic clinician. Candidates should include dentists who have experienced rotary file breakage or have the fear of rotary file breakage. The trick is to choose the right file versus progressing through several files as with rotary. Some clinicians may find this a positive while others will not. This is where the readers must test themselves against what is successful for them now. Also, if you have feared even “trying” rotary and are still manually shaping, the single file concept is truly a simple and safe entry level instrument and, who knows, you may find it is the perfect shaping method for you!

Just remember what Leonardo DaVinci said: “Simplicity is the ultimate sophistication.”

References

1. Webber J, Machtou P, Pertot W, et al. The WaveOne single-file reciprocating system. Roots. 2011;7:28-33.
2. Berutti E. Getting The Desired Results. Endodontic Practice. November 2011:62-63.
3. van der Vyver P. WaveOne Instruments: Clinical Application Guidelines.  Endodontic Practice. November 2011:45-54.
4. Berutti E, Chiandussi G, Paolino DS, et al. Effect of canal length and curvature on working length alteration with WaveOne reciprocating files. J Endod. 2011;37:1687-1690.
5. Berutti E, Paolino DS, Chiandussi G, et al. Root canal anatomy preservation of WaveOne reciprocating files with or without Glide Path. J Endod. 2012;38:101-104.
6. Ruddle C. Canal preparation single-file shaping technique. Dent Today. 2012;31:124-129.
7. West J. Nonsurgical versus surgical endodontic retreatment: “How do I choose?” Dent Today. 2007;26:74-81.
8. West J. Is the new WaveOne endodontic reciprocation for me? Dent Econ. 2011;101:32-33.
9. West JD. Endodontic Brushing: The secret to mastering rotary safety. Dent Econ. 2010; 8:44.
10. West JD. Endodontic rotary vs. reciprocation: How do I choose? Dent Econ. 2011; 6:52.
11. West JD. The endodontic Glidepath: “Secret to rotary safety.” Dent Today. 2010;29:86-93.
12. West JD. Manual versus mechanical endodontic Glidepath. Dent Today. 2011;30:136-145.
13. West JD. Glidepath implementation: “Return to the beginning.” Dent Today. 2011;30:90-97.
14. Kuttler S, Bonilla C, Perez R, et al. Evaluation of the remaining canal walls thickness and center ability after instrumentation with WaveOne reciprocating system: a CT [study in progress].

Dr. Kuttler received his dental degree in 1978 from the Universidad Tecnológica de Mexico, Mexico City, Mexico, and in 1984 Dr. Kuttler received his endodontic certificate from the University of Southern California (USC). He has been involved in academics since his graduation from USC. His major areas of scientific research interest include: the performance of nickel-titanium endodontic instruments, 3-dimensional obturation of the root canal space, root canal irrigation, and restoring endodontically treated teeth. Dr. Kuttler has presented more than 350 international courses and has lectured in more than 42 countries throughout 4 continents. He is the author of numerous scientific papers, and contributor author in 2 endodontic textbooks. Dr. Kuttler is former chair of the endodontic department and presently professor in the department of endodontics and associate dean for advanced education programs at Nova Southeastern University, College of Dental Medicine in Fort Lauderdale, Fla. He can be reached via e-mail at skuttler@nsu.nova.edu.

Disclosure: Dr. Kuttler is coinventor of WaveOne instrument (DENTSPLY Tulsa Dental Specialties).

Dr. West is the founder and director of the Center for Endodontics, Tacoma, Wash. Dr. West continues to be recognized as one of the premier educators in clinical and interdisciplinary endodontics. He received his DDS from the University of Washington in 1971 where he is an affiliate associate professor. He then received his MSD in endodontics at Boston University Henry M. Goldman School of Dental Medicine in 1975 where he is a clinical instructor and has been awarded the Distinguished Alumni Award. He has presented more than 400 days of continuing education in North America, South America, and Europe while maintaining a private practice in Tacoma, Wash. He coauthored “Obturation of the Radicular Space” with Dr. John Ingle in Ingle’s 1994 and 2002 editions of Endodontics and was senior author of “Cleaning and Shaping the Root Canal System” in Cohen and Burns’ 1994 and 1998 Pathways of the Pulp. He authored “Endodontic Predictability” in Dr. Michael Cohen’s 2008 Quintessence text Interdisciplinary Treatment Planning: Principles, Design, Implementation as well as Michael Cohen’s soon to be published Quintessence text Interdisciplinary Treatment Planning Volume II: Comprehensive Case Studies. Dr. West’s memberships include: 2009 president and Fellow of the American Academy of Esthetic Dentistry and 2010 president of the Academy of Microscope Enhanced Dentistry, the Northwest Network for Dental Excellence, and the International College of Dentists. He is a 2010 consultant for the prestigious ADA Board of Trustees where he serves as a consultant to the ADA Council on Dental Practice. Dr. West further serves on the Henry M. Goldman School of Dental Medicine’s Boston University Alumni Board. He is a thought leader for Kodak Digital Dental Systems and serves on the editorial advisory boards of the Journal of Esthetic and Restorative Dentistry, Practical Procedures and Aesthetic Dentistry, and the Journal of Microscope Enhanced Dentistry. He can be reached at (800) 900-7668, via e-mail at johnwest@centerforendodontics.com, or at centerforendodontics.com.

Disclosure: Dr. West is co-inventor of ProTaper Universal, WaveOne, and Calamus technologies (DENTSPLY Tulsa Dental Specialties).